as in treacherous
formal
causing harm in a way that is gradual or not easily noticed
Most people with this insidious disease have no idea that they are infected. an insidious enemy
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Recent Examples of insidious
But the insidious tentacles of tanking will impact the Heat – and the other Eastern Conference playoff teams – over the final six weeks of the season.
—
Barry Jackson, Miami Herald, 26 Feb. 2026
Another of measles’ worst and most insidious outcomes is subacute sclerosing panencephalitis (SSPE), an untreatable neurodegenerative condition that can take nearly a decade to manifest.
—Katherine J. Wu, The Atlantic, 24 Feb. 2026
Here, the joyous and the boisterous contrast the dark and insidious, allowing viewers to both be delighted by colorful street scenes and celebrations while the rot of fear creeps in, as the details surrounding our main character (Wagner Moura) and his predicament are revealed.
—Megan Spurrell, Condé Nast Traveler, 11 Feb. 2026
The abstracting reached its pinnacle (nadir) with an insidious Alexa ad featuring Chris Hemsworth and wife Elsa Pataky.
—Steven Zeitchik, HollywoodReporter, 9 Feb. 2026
See All Example Sentences for insidious
Barry Jackson, Miami Herald, 26 Feb. 2026
Another of measles’ worst and most insidious outcomes is subacute sclerosing panencephalitis (SSPE), an untreatable neurodegenerative condition that can take nearly a decade to manifest.
—Katherine J. Wu, The Atlantic, 24 Feb. 2026
Here, the joyous and the boisterous contrast the dark and insidious, allowing viewers to both be delighted by colorful street scenes and celebrations while the rot of fear creeps in, as the details surrounding our main character (Wagner Moura) and his predicament are revealed.
—Megan Spurrell, Condé Nast Traveler, 11 Feb. 2026
The abstracting reached its pinnacle (nadir) with an insidious Alexa ad featuring Chris Hemsworth and wife Elsa Pataky.
—Steven Zeitchik, HollywoodReporter, 9 Feb. 2026
See All Example Sentences for insidious
Recent Examples of Synonyms for insidious
Adjective
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Here, a plane crash in treacherous waters leads to survivors fending off sharks.—
Randy Myers,
Mercury News,
18 Mar. 2026
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Rescuers said the conditions were treacherous, with deep drifting snow, jagged ice and extremely limited visibility that slowed efforts to reach the man.—
Ashley Carnahan,
FOXNews.com,
18 Mar. 2026
Adjective
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The rooms Hotel Thaynes has 128 guest rooms, including six king suites, each designed for simple mountain stays with subtle pops of colors.—
Condé Nast,
Condé Nast Traveler,
19 Mar. 2026
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But eventually, nonstop quips give way to subtle observations on class, power, and, particularly during its second season, when Killface and Crews run opposing campaigns for president, the futility of electoral politics.—
Eric Vilas-Boas,
Vulture,
18 Mar. 2026
Adjective
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The problem is that such inferences are often wildly speculative and will almost certainly lead to false convictions or arrests.—
Graham Hillard,
The Washington Examiner,
20 Mar. 2026
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The defendants and company executives allegedly prepared false documents and communications to show that the company was the end user of the servers.—
Michael Sinkewicz,
FOXNews.com,
20 Mar. 2026
Adjective
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Erin Lee Opponents, however, call the measure extreme and its language deceptive.—
Austen Erblat,
CBS News,
18 Mar. 2026
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Centers' growing power Previous efforts in California, Colorado and Vermont to regulate crisis pregnancy centers arose from concerns over allegations of deceptive and misleading practices and questions about patient data privacy.—
Jazmin Orozco Rodriguez,
NPR,
18 Mar. 2026
Adjective
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The government took a genuine invitation to collaborate as a perfidious power grab.—
Gideon Lewis-Kraus,
New Yorker,
14 Mar. 2026
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For those trying to read Iran’s future, the lesson of 1953 is not just that foreign powers can be perfidious.—
Bobby Ghosh,
Time,
5 Mar. 2026
Adjective
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The application for the $100,000 life insurance policy included errors, including an incorrect Social Security number for Eric Richins, an insurance agent testified.—
Nicki Brown,
CNN Money,
17 Mar. 2026
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An earlier version of the story provided the incorrect month.—
Chaewon Chung,
Sacbee.com,
17 Mar. 2026
Adjective
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This story has been updated to correct wrong information from the Monroe County Sheriff’s Office.—
David Goodhue,
Miami Herald,
14 Mar. 2026
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So don't go off topic, don't impersonate anyone, and don't get your facts wrong.—
Damon Wise,
Deadline,
14 Mar. 2026
Cite this Entry
“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 21 Mar. 2026.
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